Numerous types of transmission systems are known for mechanically coupling driving and driven elements whose axes and planes of rotation are transversely positioned relative to one another. One such system is the worm drive transmission wherein a toothed longitudinal driving element, called a "worm," has a rotational shaft oriented at right angles to the shaft of a generally planar circular driven element, called a "worm gear." The worm gear usually has circumferential teeth that mesh with and are mechanically driven by the teeth of the worm.
Worm drives wherein the worm gear teeth are replaced by other elements such as balls or rollers, are illustrated, for example, by the arrangement shown in Nemoto U.S. Pat. No. 4,648,286. In that arrangement, spherical balls occupy recesses spaced circumferentially about a wheel at positions normally assumed by the teeth of the worm gear and are arranged to rotate within the recesses to reduce friction loss during engagement with the worm. Except for rotation about themselves, however, the balls remain fixed relative to the worm wheel, keeping the same positions and performing the same function as the traditional worm gear teeth.
Double-enveloping arrangements for worm drives exist which have the worm element longitudinally curved to assume an hourglass shape that fits the curvature of the worm gear and provides multiple-toothed contact between the elements. This configuration enables the load-carrying and horsepower capacity to be increased but is subject to potential engagement problems should the worm shift the position of its longitudinal axis relative to the worm gear. To alleviate such problems, Nemoto U.S. Pat. No. 4,651,586, for example, proposes the use of rollers mounted on radially movable, outwardly biased assemblies within the confines of radially-directed cylindrical slots located at the usual tooth locations about the worm wheel. The radial movability and rotatability of the rollers facilitates the accommodation of shifts in the worm and changes in lead angle of the worm grooves, but does not otherwise contribute to the driving-driven member drive interaction.
Transmission systems other than worm/worm gear drives are known wherein gears called "wave gears" interact by means of intermediate elements to transfer power and motion between driving and driven members. Such arrangements are disclosed, for example, in Rabek U.S. Pat. No. 3,468,175, Batty U.S. Pat. No. 3,507,159 and Ando U.S. Pat. No. 4,713,985. In a typical such arrangement, first and second wave gears having opposing periodic undulations on facing surfaces are mechanically coupled by means of intermediate carrier-supported oscillators, such as balls or rollers, which are arranged to simultaneously traverse the facing undulated surfaces of both gears. Either one of the wave gears or the oscillator carrier is moved to function as the input driving element, and either one or both of the remaining elements is made movable to serve as the driven element. Traversal of the oscillators along one of the undulated surfaces under action of the driving element drives the oscillators to be reciprocated in a direction generally normal to that surface between points of maximum and minimum amplitude. The other undulated surface is shaped so that the simultaneous contact of the oscillators with the other surface as they are reciprocated causes either the other surface or the oscillator carrier to be driven in a direction at right angles to the reciprocation and locally parallel (i.e. at points of contact with the same oscillator) to the direction in which the driving element is moved. The crests of the undulations are sometimes referred to as the "teeth" or "lobes" of the surfaces, and where the total number of such teeth on a particular surface is small, the element may be referred to as a "cam" or an "eccentric" (viz. a one-toothed or one-lobed member).
Concentric and tangential rotary arrangements, as well as linear arrangements, of wave gear transmissions are known. In each case, the drive and driven elements are locally (viz. tangentially) moved in the same or opposite parallel directions, with the oscillators reciprocating at right angles thereto. The oscillators may be of various known embodiments, including a plurality of roller members respectively riding on different ones of the undulated surfaces and being freewheeling relative to each other.
Gear arrangements in which oscillator-coupled driving and driven gear elements move tangentially in directions transverse to each other as do worm/worm gear drives, are not known to the inventor; nor are wave gear arrangements having input and output shafts transversely disposed as in worm drives. Likewise, oscillator means traversing opposing undulated surfaces, like those employed in wave gear drives, are believed not heretofore known in worm drive arrangements.